AMD Radeon 6870HD crashes all games after update to 15.7.1

I have two of these cards in Crossfire which have been stable and perfect for a very long time.

After updating to 15.7.1 one of the cards instantly started giving me graphical errors such as incorrect colours (even during boot). It would get past the windows logo and then just hang on a blank grey-black screen, it would not go to the welcome screen.

I rolled back the driver in safe mode and the problem persisted.

I removed the auxiliary card and it still happened so I took out the one which had always been primary and put the second one in its place.

Now I can boot into windows on the one card but whenever I try to play a game the 'Display Driver has stopped responding but has recovered' message appears accompanied by flashing screens and artifacts such as lines.

After flashing on and off a few times, I get a BSOD accompanied by a message about a video refresh timer taking too long to reset.

There appears to be nothing I can do.I can use windows and all programs within perfectly, but all games cause a BSOD after a few flashes of the failure message.Firstly, it seems my first card has been pushed over the edge into death by something taxing or new (I'm not entirely surprised it is 4 years old now and was possibly due to go anyway) but secondly .. what the hell with the games?